Luminous discharge cell for spectrographic analysis

ABSTRACT

The cell has an anode with a light-transmitting through bore, one end of which is directed towards a sample-supporting cathode, the other end being directed towards a window in an anode housing. An electrically insulating sleeve is interposed between the anode and the housing. The sleeve is slidable along the anode and surrounds the end of the anode which faces the cathode. The annular end of the sleeve can be applied against a seating surface of the sample support.

United States Patent Ferre et a1.

1 51 Sept. 30, 1975 LUMINOUS DISCHARGE CELL FOR SPECTROGRAPHIC ANALYSIS Inventors: Salvador Ferre. Massy; Dan Lotan.

Paris; Rene Jean Morhioli, Chcnnevieres; Jean-Claude Alphonse Henri Schmitt, Sainte-Genevie\'e-des-Bois; Jean-Louis Cordazzo Dammarie-les-Lys, all of France Assignee: Ste. Nationale d'Etude et de Construction de Moteurs dAviation, Paris, France Filed: July 3, 1974 Appl No.: 485,452

Foreign Application Priority Data July 6, 1973 France 73.24891 Apr. 30. 1974 France 1. 74.14940 US. Cl. 313/146; 313/209; 356/86 Int. Cl.'-.... GOIJ 3/30; H011 1/88; H01J 17/04 [58] Field of Search 313/146. 209. 231.7; 356/86 [56] References Cited UNITED STATES PATENTS 3,619.062 11/1971 Heres et a1 356/86 3.626134 12/1971 Grimm 356/86 X 3.631990 1/1972 Baierlein.. 356/86 X 3,699,383 10/1972 Chaney 313/209 X Primary E.\'aminerPalmer C. Demeo 21 Claims, 7 Drawing Figures 6 4 Mafia/38,512 l0 7 5-] 55b US. Patent Sept. 30,1975 sheet 3 of3 3,909,652

LUMINOUS DISCHARGE CELL FOR- SPECTROGRAIHIC ANALYSIS The present invention concerns a luminous discharge cell for spectrographic analysis. I v

The invention relates especially to a cell for analysis in a rarefied gas, compris ing asample support; a sealed chamber which is defined by walls and into which open a supply conduit for gas and a pumping conduit;'a cathode which is connected to the negative pole; of an electric generator; an anode which is connected to the posi In a known cell ofthis type the cathodeis-hollow andconstitutes the support wall of the cell. The support for the sample to be analysed, which constitutes the cathode bottom is applied sealingly to the support wall bymeans of a toroidal seal. The body of this known cell is provided with a tip penetrating into the body of the cathode. l 7 I By reason of the design and the geometry of this known cell, metallic beads tend to form by reason ofthe electrical discharge, imainly. radial, set up between anode and cathode, with the risk that short circuits will be produced, rendering the results'of analysis unreliable and thus limiting the performance graphic apparatus. v

Moreover, in this known cell,'the presence of the toroidal seal between the sample support and the support wall constitutingjthe cathode means that the-electrical contactbetween the sample support and the wall is not complete. To produce complete contact it would be necessary to use a strong spring thrusting the sample support against the cathode wall, which would mean unwanted crushing of theseal. Moreover, it the sample support has'a bent shape, inorder to produce effective sealing betweenthe sample support. and the support surface and to produce good electrical-contact, it is necessary to use intermediate pieces of complicated shape with toroidal seals of suitable shape As a result the use of this known cell is difficult and limited- The object 1 of the present invention is a spectrographic analysis cell eliminating or at least reducing undesired electrical discharge between anodeand cathode and allowing a wide 'range of qualitative and'quan titative spectrographic analyses to be carried out on-a variety of materials, with low consumption of the materials. Y Y I I In accordance with the invention, the sample support is'connected to the negative pole of the electric generator by conductive means separate from-the support wall of the cell, but withinterposition,between the end of theanode adjacent the cathode and an adjacent wall of.-

the cell,- of an .insulating sleeve which surrounds the said end of the anode which can slide along the-anode, and which can be. applied by an annular face against the face. turned towards the anode, of the sample support.

Thus in this cell the end of the insulating sleeve rests on the cathode, whichmay or'maymot be flatand.

of the spectro-v which constitutes thesupport for the sampleto'be analysed, with the result that this insulating sleeve pre cisely defines the area with which the analysis is concerned. The insulating sleeve ensures sealed connection against electrical discharge, on the one hand with the sample support and on the other hand with the body of the anode in'such a manner as to define, with the internal face of the bore of the anode and the inner face of the. sample support, the cell chamber.

In a preferred embodiment of the cell gas passes through the bore of the anode and returns through axial passages provided along'at least a portion of the length of the anode. Such axial passages are for instance made by machining the external surface of the anode.

Other characteristics and advantages of the invention will be better understood from the following description of several embodiments of the invention, given by way of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a view in axial section of one embodiment of luminous discharge cell;

FIG. 2 is a view, on a larger scale, in cross section of the anode of the cell shown in FIG. 1;

FIG. 3 is a part view in axial section'of another embodiment of cell;

FIG. 4 is a view in axial section of another embodiment of cell;

FIG. 5 is an exploded sectional view of the insulating sleeve, thesample support, and the electrical connection rod of the cell shown in FIG. 1;

FIG. 6 is an exploded sectional view of an alternative embodiment of the insulating sleeve, the sample carrier, and the electrical connection rod; and

FIG. 7 is an exploded sectional view of a further alternativeembodiment of the insulating sleeve, the sample carrier and the connection rod.

FIG. l shows a luminous discharge cell for spectrographic analysis ha'ving a sealed cell chamber 1, into which opens a supply conduit 2 for a neutral gas such as argon and a pumping conduit 3 connected to a pumping unit (not shown). The cell has a cathode connected to the negative pole of an electric generator (not shown) and an anode 4 connected to the positive pole of the electric generator. The anode 4 is constituted by a metal tube with a rectilinear bore 4a which extends through it from one end to the other; the bore 4a opens out at one end towards a support .5 for the sample to be analysed, and at the other end towards a transparent window 6.

The cell shown also has means for applying the internal face 5a of the sample support 5 sealingly against the annular sealing face 7a of an annular metal support wall -7 electrically insulated fromthe anode 4, in such a mannerthat the sample support 5 defines the cell chamber 1. The annular support wall 7 is cooled by water circulation, symbolised in FIG. I by the arrow f,.

The cathode of the cell is constituted by the sample support 5 alone, which is connected to the negative pole of the electric generator by means of conductors separate from the annular support wall 7 of the cell.

Moreover, between the end of the anode 4 and the support wall 7 is interposed a continuous insulating annular wall or sleeve 8,'which is fitted on and surrounds the end of the anode 4, and is mounted on the anode so as to be slidable axially parallel to the axis of the bore 4a of the anode 4; the entire annular end face 8a of the sleeve 8 is applied against the internal face 511 of the sample support 5. The sleeve 8 is easily replaceable.

The annular support wall 7 is housed and fixed in a cell body 9 of Plexiglass (a Trade Mark for methyl methacrylate polymer) or another insulating material. In the example of FIG. 1, where the wall 7 is of metal. it has an insulating envelope 10, for example of Tefion (a Trade Mark for polytetrafluoroethylene). ln'

the interior of the envelope 10, which is for instance fitted tightly in an axial bore of the wall 7,the sleeve 8 can slide axially. The sleeve 8 can be made of quartz or another electrically insulating material of good thermal behaviour.

A compression spring 11 is interposed between the end of the insulating sleeve 8 and a shoulder provided on the anode 4 and is arranged to thrust the insulating sleeve Sagainst the sample support 5. The spring also facilitates the extraction of the sleeve 8.

The anode 4, which is made for instance of copper, is mounted in the cell so as to be axially displaceable.

The anode is screw threadedly engaged with a support 14. Displacement of the anode iseffected by means of a worm 13 and worm-wheel 12 rigid with the anode 4. Rotation of the worm 13 on its spindle 13a causes rotation of the screw-threaded anode 4 inits support 14 and thus brings about the axial displacement of the anode. The spindle 13a extends outside the cell, thus making it possible to effect from the outside the regulation of the axial position of the anode 4, and consequently the spacing between the anode 4 and the cathode (sample support The anode 4 and the sleeve 8 can easily be dismantled and replaced by similar members having different dimensions. It is advantageous for the sleeve 8 to be long enough to permit spacings of some tenths of a millimetre to several centimetres between the anode 4 and the sample 5. It is thus possible, by suitably regulating this spacing, to achieve the best conditions for analysis by limiting the vapourisation of the sample between the two electrodes.

The window 6 is either a plate with parallel faces (a quartz plate in the example shown) or a non-absorbent tive powder 56 (e.g. graphite) the surface 5a of which.

supportsthe particlesto be analysed (not shown).

A centering and cooling member .18 is used, in partic ular when the sample support 5 is flexible or has small dimensions. If it is rigid a spring 16 will be sufficient to apply it against the wall 7. Cooling is ensured by water circulation j? in the member 18.,

FIG. 3 shows an embodimentof cell particularly adapted for the study of curved surfaces. A washer or intermediate piece 19 is fitted on one end of the insulating sleeve 8 and is applied sealingly by means of toroidal seals 20, 21 respectively against the sealing face 7a of the support wall 7 and against the face 5a of the sample support 5.

The discharge cell described above, in view of the regulating possibilities, the interchangeability, the ease of access, and the easy cleaning of all its constitutent parts, can be adapted to numerous analytical problems.

, In particular, as concerns the analysis of solids, it can lens; its purpose is to allow the luminous radiation from g the sample to pass a spectrograph (not shown).

It will be observed that the possibilities of regulation offered allow various exposure times, in particular extended exposure times and also the use of differentcurrent strengths. Such possibilities ensure great exploitation of spectrometric measurement apparatus used for analysing the light emitted by the cell.

The gas, for instance argon, is introduced into the cell through the conduit 2, passes, along the axial bore 4a and then returns between the anode 4 and the sleeve 8 through channels made either in the external face of the anode 4, as in the case of the channels 30 shown in FIG. 2, or in the internal face of the sleeve 8, or through any other suitable cavities, the anode 4 being fitted with play in the sleeve 8. The gas pressure in the cell chamber 1 is maintained at a suitable value, between 2 mm and 30 mm of mercury, by means of a pump connected to the conduit 3. Gas-tight sealing between the sample support 5 and the sealing face 7a is effected by means of a toroidal seal '15.

The anode support 14 is cooled by water circulation, symbolised in FIG. 1 by the arrow f The supply of electrical current to the anode is effected by means of the support 14, through a terminal 14b.

The sample support 5 in the embodiment shown comprises a copper ring 5b enclosing a mass of conduciting vapourisation, of effecting several quantitative analyses on the same particle of small dimensions, in

particular on particles collected in the oil filters of muchines.

ln fact, the wear on rotating piecesin an engine manifests itself inter alia by the transference to the lubricating oil of metal particles of very different sizes and shapes; some of these remain in suspension in the oil, othersmay beretained by filters arranged in the oil circuits.

' It is of particular interest in aviation to follow the development of wear phenomena inengines by the analysis of solid particles carried along by the oil in operation. The analysis of these particles and the knowledge, ofthe constituent materials greatly facilitate the pinpointing of damage. The analysis is carried out after the particle has been coated by means of a conductive powder forming an electrically conductive disc used as cathode. An automatic disc manipulation device can be produced for presenting particles successively for analysis.

Finally, because of the possibility of carrying out n0ndestructive analyses, the cell can also find application in checking the nature of the surface of finished pieces. 7

Alloys as well as non-metallic materials may contain a very small quantity (0.1 p.p.m. to l p.p.m.) of metallurgical components or impurities, and it is difficult to determine these by known methods.

The luminous discharge cell forming the subject of the invention has particularly interesting application when it is a question of determining volatile elements in a refractory-based alloy. Alloys on a basis of nickel, for instance, can be contaminated by bismuth, tin, lead, or silver.

The bismuth may notably come from a material (lowmelting-point alloy) used for coating casting in order to facilitate their machining, and should not exceed .1 p.p.m. One of these materials, used commercially under the name of CERROBAND, is used in particular in operations of pinning the feet of vanes.

The embodiment described below with reference to FIGS. 4 to 7 is an adaptation of the luminous discharge cell described above, to enable analysis of these volatile elements to be undertaken with great ease.

For this purpose, a hollow sample carrier 50 is fitted in the end of the insulating sleeve 8 and opens into the sleeve 8 through an orifice 50jcoaxial with the sleeve. The orifice 50 has a cross-sectional area less than that of the mid-section of the cavity of the sample carrier 50.

Accordingly, in this cell, the volatile elements are confined in the cavity of the sample carrier and the analysis carried out is more accurate.

FIG. 4 also shows a sealed cell chamber 1 into which opens a supply conduit (not shown) for a neutral gas, such as argon and a pumping conduit (not shown) connected to a pumping unit. The cell has a cathode connected to the negative pole of an electric generator (not shown) and an anode connected to the positive pole of the generator. The anode is constituted by a metal tube 4 having a rectilinear bore 4a which passes through it from one end to the other; one end faces the sample carrier 50 containing the sample 50m to be analysed and the other end faces a transparent window (not shown).

The sealed non-conductive chamber 1, for instance of PYREX (a Trade Mark for methyl methacrylate polymer) is defined on the sample side by a cooled wall 18, which carries and surrounds the sample carrier 50 and whose free edge 18a is applied sealingly against an adjacent cooled annular support wall 7 of the cell. The sample carrier 50 and the wall 18 together constitute the sample support of the cell.

Moreover, between the support wall 7 and the end of the anode adjacent the sample carrier is interposed an insulating annular wall or sleeve 8, which is fitted on and surrounds the said end of the anode 4. The sleeve 8 is axially slidably mounted on the anode 4, and its annular end face 8a (preferably the entire extent of this face) is applied against a shoulder 50a on the sample carrier 50.

The wall 7 is of metal and has an insulating envelope 10, of Teflon for instance. In the interior of the envelope 10, which is for instance a force fit in an axial bore of the wall 7, the sleeve 8 can slide axially. This sleeve is easily interchangeable and can be made of quartz or another electrically insulating material of good thermal behaviour.

A compression spring (not shown) can be interposed between the insulating sleeve 8 and a shoulder (not shown) on the anode 4 so as to thrust the sleeve 8 against the sample carrier 50.

The anode 4, for instance of copper, is mounted in the cell so as to be axially displaceable, in the manner described above, for example, so that axial displacement can be effected from outside the cell, to regulate the axial position of the anode 4 and consequently of the sample carrier 50.

The anode 4 and the sleeve 8 can easily be dismantied and replaced by similar members of different dimensions. It is advantageous for the sleeve 8 to be of such length that the spacing between anode 4 and cathode sample carrier 50 is some tenths of a millimetre to several centimetres.

The support wall 7 has been modified to receive the cooled wall 18 of PYREX, the sealing being effected by means of a toroidal seal 100.

In the embodiment of FIG. 5 the sample carrier 50 is hollow and is constituted of two parts 50a and 50b made of graphite. The part 50b has a bore 504 which receives with slight play a conductive rod 16 made of tungsten, and has a recess 50h intended to contain the sample to be analysed, which is generally in the form of powder or chips.

The end 50k of the part 50bfits with slight play in a bore 50c made in the part 50a, which is itself fitted in the sleeve 8. The cross-section of the orifice 50 jof the part 50a is smaller than that of the recess 50!: in the part 50b.

FIGS. 6 and 7 show, in exploded view, similar to the exploded view of FIG. 2, two variants of assembly of the sample carrier 50.

The sample 50m to be analysed is arranged in the interior of the hollow sample carrier 50 which is then fitted in the end of the insulating sleeve 8. The cavity of the carrier communicates with the interior of the sleeve 8 through the orifice 50j, 50j, coaxial with the sleeve 8 and having a cross-section less than the average cross-section of the 50h, 50h of the sample carrier 50.

In order to carry out the analysis of the volatile elements, one focuses in the outlet plane 50! of the sample carrier 50.

The base metal of the sample, for instance the nickel, is generally less volatile and makes only slight appearance in the analysis.

The cell described above has notably the following advantages:

one can reuse the electrode after the sample carrier and the sleeve have been cleaned;

the electrical discharge is channelled parallel to the axis and can thus be concentrated on the sample to be analysed;

the volatile elements are confined in the graphite sample-chamber constituted by the part 50b and analysis is sensitive;

the cell is easier to use than known cells, since only a few minutes are needed for changing or cleaning the sample carrier 50.

We claim:

1. A luminous discharge cell for spectrographic analysis, comprising a sample-supporting cathode, an anode housing having a window, an anode having at least one light-transmitting through-bore, one end of which is directed towards the cathode, the other end being directed towards the window, and an electrically insulating sleeve interposed between the anode and the housing and surrounding the end of the anode facing the cathode, the sleeve having an annular end and being slidable along the anode, said annular end being arranged, to be applied against a seating surface of the sample supporting cathode, said anode housing and said sample supporting cathode defining a sealed cell chamber, an ionisable gas being enclosed inside said sealed chamber.

2. A cell as claimed in claim 1, further comprising a compression spring interposed between the insulating sleeve and a shoulder provided on the anode, to thrust the insulating sleeve against the sample supporting cathode.

3. A cell as claimed in claim 1, further comprising a mounting member in which the anode is screwthreadedly engaged, and means for rotating the anode relative to the mounting member so that the anode is displaced selectively towards and away from the cathode.

4. A cell as claimed in claim 1, in which the cathode bears against a metal support wall of the anode housing, the support wall being electrically insulated from the anode by means of an envelope of electrically insulating material resistant to heat interposed between the support wall and the insulating sleeve, the sleeve being axially slidable in the envelope.

5. A cell as claimed in claim 1, in which the sample supporting cathode is connected directly to an electrical supply conductor for connection to an electric generator.

6. A cell as claimed in claim 1, further comprising electrically conducting means for supporting the sample supporting cathode and for connecting the cathode to an electric generator.

7. A cell as claimed in claim 1, in which the anode and the insulating sleeve are removable.

8. A cell as claimed in claim 1, including a passage for circulation of gas along the part of the anode enclosed by the insulating sleeve.

9. A cell as claimed in claim 8, in which the passage is formed in the anode.

10. A cell as claimed in claim 8, in which the passage is formed in the external surface of the anode.

11. A cell as claimed in claim 8, in which the passage is formed in the internal surface of the sleeve.

12. A cell as claimed in claim 8, in which the anode fits loosely in the sleeve.

13. A cell as claimed in claim 1, in which the sample supporting cathode is applied sealingly to a support wall of the anode housing.

14. A cell as claimed in claim 1, in the sample supporting cathode comprises a hollow sample carrier fitted in the end of the insulating sleeve, the sample carrier opening into the sleeve through an orifice which is substantially coaxial with the sleeve and which has a cross-sectional area less than the average crosssectional area of the interior of the samplecarrier.

15. A cell as claimed in claim 14, including a wall which supports the sample carrier and which is applied sealingly to the anode housing.

16. A cell as claimed in claim 14, in which the sample carrier comprises a body having a blind longitudinal bore atone end remote from the insulating sleeve, the bore receiving the end of an electrically conductive rod to be connected to the negative pole of an electric generator, and blind bore to receive 'a sample to be analysed.

17. A cell as claimed in claim 16, in which the sample carrier comprises two interfitting parts, one being the said body, the other being a sleeve fitting on the one hand on the body and on the other hand on the insulating sleeve.

18. A cell asclaimed in claim 16, in which the sample carrier comprises two parts, one being the said body.

the other capping the body and having an axial opening, the end having the axial opening being applied sealingly to the insulating sleeve.

19. A cell as claimed in claim 16, in which the sample carrier consists of a single piece which fits in the insulating sleeve.

20. A cellas claimed in claim 14, in which the sample carrier supporting wall has a vacuum connection point. 21. A cell as claimed in claim 14, in which the sample carrier supporting wall is cooled.

l l= =l l UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,909,652 DATED I September 30, 1975 lN\/ ENTOR( I Salvac io Ferre, et a1 it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line "is flexible or" should be deleted Signed and Scaled this Fourth D a) of October I 977 [SEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Officer Acting Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,909,652 DATED September 30, 1975 |NVENTOR(5) 1 Salvado Ferre, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 29 "1" should be "4-- line 28, "the" (second occurrence) should be --aline 63, before "bismuth" should be --metals such as-- Column 5, line 15, "accurate" should be --sensative- Signed and Scaled this Fourth D3) of January 1977 [SEAL] A ttes t.

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner; ofPaIenIs and Trademarks 

1. A luminous discharge cell for spectrographic analysis, comprising a sample-supporting cathode, an anode housing having a window, an anode having at least one light-transmitting throughbore, one end of which is directed towards the cathode, the other end being directed towards the window, and an electrically insulating sleeve interposed between the anode and the housing and surrounding the end of the anode facing the cathode, the sleeve having an annular end and being slidable along the anode, said annular end being arranged, to be applied against a seating surface of the sample supporting cathode, said anode housing and said sample supporting cathode defining a sealed cell chamber, an ionisable gas being enclosed inside said sealed chamber.
 2. A cell as claimed in claim 1, further comprising a compression spring interposed between the insulating sleeve and a shoulder provided on the anode, to thrust the insulating sleeve against the sample supporting cathode.
 3. A cell as claimed in claim 1, further comprising a mounting member in which the anode is screwthreadedly engaged, and means for rotating the anode relative to the mounting member so that the anode is displaced selectively towards and away from the cathode.
 4. A cell as claimed in claim 1, in which the cathode bears against a metal support wall of the anode housing, the support wall being electrically insulated from the anode by means of an envelope of electrically insulating material resistant to heat interposed between the support wall and the insulating sleeve, the sleeve being axially slidable in the envelope.
 5. A cell as claimed in claim 1, in which the sample supporting cathode is connected directly to an electrical supply conductor for connection to an electric generator.
 6. A cell as claimed in claim 1, further comprising electrically conducting means for supporting the sample supporting cathode and for connecting the cathode to an electric generator.
 7. A cell as claimed in claim 1, in which the anode and the insulating sleeve are removable.
 8. A cell as claimed in claim 1, including a passage for circulation of gas along the part of the anode enclosed by the insulating sleeve.
 9. A cell as claimed in claim 8, in which the passage is formed in the anode.
 10. A cell as claimed in claim 8, in which the passage is formed in the external surface of the anode.
 11. A cell as claimed in claim 8, in which the passage is formed in the internal surface of the sleeve.
 12. A cell as claimed in claim 8, in which the anode fits loosely in the sleeve.
 13. A cell as claimed in claim 1, in which the sample supporting cathode is applied sealingly to a support wall of the anode housing.
 14. A cell as claimed in claim 1, in the sample supporting cathode comprises a hollow sample carrier fitted in the end of the insulating sleeve, the sample carrier opening into the sleeve through an orifice which is substantially coaxial with the sleeve and which has a cross-sectional area less than the average cross-sectional area of the interior of the sample carrier.
 15. A cell as claimed in claim 14, including a wall which supports the sample carrier and which is applied sealingly to the anode housing.
 16. A cell as claimed in claim 14, in which the sample carrier comprises a body having a blind longitudinal bore at one end remote from the insulating sleeve, the bore receiving the eNd of an electrically conductive rod to be connected to the negative pole of an electric generator, and blind bore to receive a sample to be analysed.
 17. A cell as claimed in claim 16, in which the sample carrier comprises two interfitting parts, one being the said body, the other being a sleeve fitting on the one hand on the body and on the other hand on the insulating sleeve.
 18. A cell as claimed in claim 16, in which the sample carrier comprises two parts, one being the said body, the other capping the body and having an axial opening, the end having the axial opening being applied sealingly to the insulating sleeve.
 19. A cell as claimed in claim 16, in which the sample carrier consists of a single piece which fits in the insulating sleeve.
 20. A cell as claimed in claim 14, in which the sample carrier supporting wall has a vacuum connection point.
 21. A cell as claimed in claim 14, in which the sample carrier supporting wall is cooled. 